This invention concerns catalytic compositions suitable for a hydrosilylation of polyorganosiloxane, particularly catalytic compositions suitable for crosslinking reaction of addition-reaction type silicone elastomers.
It is known that catalysts of the platinum group have, conventionally, been used for hydrosilylation reactions, that is, the addition-reaction between compounds with an aliphatic unsaturated bond and compounds with a Si--H bond. They are also known to be effective as curing catalysts for so called addition-reaction type polysiloxane compositions which are composed of polyorganosiloxane with an olefin aliphatic unsaturated bond and polyorganosiloxane with a Si--H bond, and which forms a polyorganosiloxane elastomer with a network structure by hydrosilylation reaction between the two siloxanes. These platinum catalysts have the following advantages: (1) curing reaction time is extremely short; (2) a small amount of catalyst is effective, and only a minute amount of catalyst or its decomposed product remains in the product obtained.
These platinum catalysts, however, may cause instability in the products containing them due to their ability to promote the addition-reaction referred to previously at normal temperatures. This imposes considerable limits on fabrications requiring storage time between processes or time for freshening, extrusion, or insertion into a mold after the catalyst is added and before curing. This has been the limiting factor in using the addition-reaction type polysiloxanes employing platinum catalysts, especially when they are used in the same application as heat-vulcanizing type silicone rubber using conventional organic peroxides as catalysts. Many methods have been suggested which aim at inhibiting the activity of a catalyst at room temperatures. There are methods, for example, to add acetylene compounds (Japanese Pat. No. 31476 issued 1969,), nitrile compounds (Japanese Pat. No. 22018 issued 1970,), and sulfur compounds (Japanese Pat. No. 1116 issued 1972,) as inhibitors to platinum catalysts such as platinic hydrochloride Control of the amount of inhibitor to be added, however, is delicate, and an excess amount leads to insufficient curing and too small an amount leads to an insufficient inhibiting effect on catalytic activity, which hampers the stability of the compositions. Further, there are some types of inhibitors whose effect is weakened as a result of evaporation during storage, or the heat resistance or electrical properties of the silicone rubber obtained are adversely affected by the inhibitor which remains after curing. The method using a divalent platinum-phosphorus complex (Japanese Pat. No. 19193 issued 1969,) does not produce a sufficient inhibiting effect. The use of a zero valent platinum-phosphorus complex have a superior inhibiting effect, (Japan Patent lay-opened 1976, No. 139853) but their practical application is limited due to their instability against oxygen and heat, which requires special precautions during storage and use; long storage at a temperature over 40.degree. C. must especially be avoided. This invention eliminates these limitations on the practical application of platinum catalysts and provides a catalyst composition which has stability, and long storage, the present invention provides good catalytic compositions suitable for a hydrosilylation reaction of polyorganosiloxane and is, especially suitable for a crosslinking reaction of addition-reaction type silicone rubber compositions.